1. Field of the Invention
The invention concerns a process for manufacturing compositions of thermoplastic materials having an elevated gas impermeability and/or certain improved physical and mechanical properties which can be used for example in the field of packaging carbonated liquids.
2. Description of the Prior Art
Certain uses of plastic materials require a very high gas impermeability. It is also known that this impermeability is selective and that it varies unpredictably. The gas permeability coefficients of a given plastic material may differ enormously depending on the particular gas. It should likewise be noted that these differences can be complemented, for example a plastic material can be permeable to gas A and impermeable to gas B whereas the complementary material could be impermeable to gas A and permeable to gas B. Thus it seems normal to combine these two materials in order to obtain a composition having a high impermeability coefficient with respect to both gases A and B.
It often occurs that the materials which one wants to combine are incompatible. This results, for example, in the coextrusion of multilayered complexes, in a product which tends to peel apart quasi-spontaneously and is thus not suited for applications requiring a minimum amount of cohesion and adherence.
This manifests itself further when, for example, a mixture of incompatible polymers are extruded, in the manufacture of a product having a non-homogeneous structure of composition. This heterogenity can be seen with the naked eye or with a magnifying glass or occasionally with the aid of a high-power microscope. The product obtained thus has a structure which resembles that of an emulsion or of a solidified suspension having a continuous as well as a discontinuous phase. If the permeability of this product is measured, it is found that it is approximately that of the continuous phase. The benefit of the reduction in permeability which the polymer in the discontinuous phase would have been able to add, which would have been desirable for certain applications, is not achieved.